Conventionally, a technique of forming a pn junction diode by using a diamond semiconductor has been known (refer to Non-Patent Document 1). In a diamond semiconductor, an energy level of conductive impurities is located at a deep position beyond a thermal excitation energy at an operating temperature. Specifically, an acceptor and a donor having the shallowest energy levels are B (boron) and P (phosphorus), respectively. However, energy levels of B and P are 0.37 eV and 0.6 eV, respectively, and are greater than 0.026 eV, which is a thermal excitation energy under standard conditions, by one order of magnitude or more. For this reason, a diamond semiconductor cannot have a high carrier density, and hence has an extremely large resistance value. As a result, it is extremely difficult to cause a high density current to flow through a pn junction element formed of a diamond semiconductor. Specifically, the diamond pn diode disclosed in Non-Patent Document 1 has a current density of at most approximately several A/cm2 (8V). This value is lower than that of a pn junction diode formed of silicon carbide, or the like, by two orders of magnitude or more.
The present invention has been made in view of the above-described problem, and an object of the present invention is to provide a semiconductor device which allows a high density current to flow therethrough.
Non-Patent Document 1: M. Kubovic et al., Diamond & Related Materials, Vol. 16 (2007) pp. 1033-1037